The Mercedes CLS63 AMG had the optional Performance Package with larger brakes and wheels.

Time Hockenheim

M5: 1m 16,8 s
CLS63 AMG: 1m 18,5 s

Mercedes is unprecize and the M5 have higher entrance speed.

Base price
M5: €92 500
CLS63 AMG: €104 720

0-100 km/h
M5: 4,7 s
CLS63 AMG 4,7 s

0-200 km/h
M5: 14,3
CLS63 AMG: 15,4 s

18 m slalom
M5: 66 km/h
CLS63 AMG: 61,9 km/h

Minimal fuelcunsumption
M5: 1,34 l/ 10 km
CLS63 AMG: 1,45 l/10 km

Maximal fuelconsumption
M5: 2,14 l/10 km
CLS63 AMG: 2,28 l/10 km

Average fuelconsumption
M5: 1,64 l/ 10 km
CLS63 AM: 17,7l/10 km

Total sum of points:

BMW M5: 46
CLS63 AMG: 36

The largets difference between the points where the Slalom track, where BMW M5 got 8/10 and Mercedes 2/10. Also, despite the Performance Package upgraded brakes on the CLS63 AMG it receives 5/10 for braking 100-0 meters, as opposed to the M5 which receives 8/10. Mercedes looses points vs the M5 in categories Hockenheim, price/performance ratio and Driving fun. The only category which the BMW M5 looses to the CLS63 AMG is everydaydriving with one point, where Mercedes receives 9/10 and BMW 8/10.

Will the M5 still be able to see it off as easily or will it be a battle the M5 can't win. I think the M5 will still win the position of Driver's choice (rwd = no brainer) but ultimately it will lose to the RS6 on pure performance.

It will be hard to argue against 580hp and 650Nm of torque, regardless of it's weight.